Storm drains and guttering gushed while rivers of rain water ran down Singapore's streets on Friday as storms lashed the city-state, doing little to ease Formula One drivers' concerns ahead of the night race.

The first practice session for the sport's inaugural floodlit grand prix is due to take place at 1900 local time (1100 GMT) later on Friday.

Meteorologists had predicted a 50 percent chance of rain over the weekend and drivers have already voiced some concern about the combination of rain, floodlights and an untested street circuit.

"I think the biggest thing really is if we have a downpour and knowing what it's going to be like in the spray with the light refracting through the water," Red Bull driver David Coulthard told reporters.

"We don't know how much it's going to hang in the air, so that would be the most difficult thing I think."

Sauber's Nick Heidfeld [Images] echoed Coulthard's thoughts. "I would have welcomed the chance to test on the track, especially in the rain," he told reporters.

"Rain combined with the artificial light is the great unknown for me with this race.

"The climate should be similar to that in nearby Kuala Lumpur, and -- from experience -- it rains frequently there, especially in the early evening."

TROPICAL CONDITIONS

Heidfeld's teammate Robert Kubica [Images] added: "There are still some question marks regarding weather conditions and, related to the chance of rain, the light situation.

"I am sure the (sport's governing body) FIA have done everything to make it a safe race."

Championship leader Lewis Hamilton [Images] has said he would rather the race be in the dry, saying that would make things "easier".

But the Briton, who leads the drivers' standings by one point from Ferrari's [Images] Felipe Massa [Images] with four races to go, has not expressed any anxiety about the expected rain.

His chief executive at McLaren Martin Whitmarsh is less blas� about the problems rain poses, however.

"If it rains, there is the unknown of whether there will be a problem with glare or the sparkle of light from droplets of rain that is greater than you would ordinarily get," he said.

"To manage this we are using coatings for the visors that won't allow droplets to collect."

Williams's Japanese driver Kazuki Nakajima also acknowledged the difficulties the tropical conditions could pose.

"We've been doing quite a bit of work in our simulator in preparation for this race and it looks like Singapore could be quite a complex circuit with lots of corners, but it should still suit our car," he told reporters.

"I don't think driving at night will be a problem if it's dry but, if it's wet which it looks like it will be, it could be quite difficult with the reflection."